This invention relates to a fluorescent x-ray analyzer.
A fluorescent x-ray analyzer of a so-called bottom lighting type is characterized as having an x-ray source disposed below a sample table for supporting a sample thereon such that the primary x-ray emitted from the source will be made incident onto an opening at a specified position on the sample table. If a sample is placed at this specified position and the primary x-ray beam from the source is made incident thereon through the opening, a secondary x-ray beam is generated on the lower surface of the sample and this secondary x-ray beam is analyzed by means of a detector such as a semiconductor detector to obtain measured data.
Some of such fluorescent analyzers are equipped with a sample table capable of not only carrying thereon a plurality of samples to be analyzed but also transporting a selected one of them to a specified position for analysis. A typical example of sample table of this kind comprises a rotatable disk-shaped member referred to as a turret, having a plurality of openings at equal distances from the center of this disk Each of the openings has a sample position associated therewith such that the turret is rotated a sample is selected.
With a fluorescent x-ray analyzer provided with a turret structured as above, the height of the target surface to be measured will generally change with respect to a reference surface, depending on which of the sample positions is disposed at the position for measurement. If this height changes, both the path length of the primary x-ray beam from the source to the bottom surface of the sample and that of the secondary beam from the bottom surface of the sample to the detector will also change. A change in the path length of the primary beam means that the intensity of the primary x-ray beam changes on the bottom surface of the sample and hence that the intensity of the secondary beam will change accordingly. A change in the path length of the secondary beam means that its intensity is not constant as it is received by the detector. In other words, even if primary beams of the same intensity are used to analyze the same sample, there will be variations in the signals outputted from the detector, depending on the position of the sample placed on the turret. For this reason, it has been a common practice in the production of a turret to minimize the differences among the heights of the sample positions.
This may be done, for example, by using primary beams of the same intensity and the same sample to measure the intensities of the signals outputted from the detector as the sample is moved from one sample position to another. If the error is expressed in terms of the ratio between the amplitude of the variations and the average signal intensity, an error as small as about 0.02-0.3% is usually required for a fluorescent x-ray analyzer of a medium capability. In order to reduce the error to this level the differences in height at different sample positions must be within a range of several to several tens in units of .mu.m. Thus, it has been necessary to use not only an expensive high-precision machine for the production of a sample table with a turret but also a micro-gauge or the like to assemble the produced parts with a high degree of accuracy. It now goes without saying that the use of such apparatus adds to the production cost.
It should be appreciated that a problem of this kind is not unique to fluorescent x-ray analyzers but may well come about with fluorescent x-ray analyzers of different types. In the case of a fluorescent x-ray analyzer with a so-called X-Y stage or an r.theta. stage adapted to two-dimensionally move the sample position with respect to the x-ray source, the distance between the x-ray source and the target surface for the measurement is likely to vary, depending on the position at which the sample is placed.